HIV-1 Strain and Primary Drug Resistance in Canada

Surveillance Report to June 30, 2001

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Results at a Glance

This report is organized into a summary page followed by four further sections. The first section provides an overview of Health Canada's Canadian HIV Strain and Drug Resistance Surveillance Program (CHSDRSP). The second section describes primary drug resistance in Canada as determined by the CHSDRSP and summarizes results from other key studies conducted in Canada, the United States, and Western Europe. The third section describes HIV-1 subtypes in Canada as determined by the CHSDRSP. The fourth section describes HIV subtype results from the sentinel surveillance arm of the CHSDRSP, which helps the provincial health laboratories with the testing and identification of samples from individuals with unusual clinical manifestations and/or with unusual laboratory results.

Summary of the Main Findings

• The overall prevalence of primary drug resistance to at least one anti-retroviral drug is 5.9% in the sample population of 481 newly diagnosed individuals who had never received treatment.

• Multi-drug resistance to the nucleoside reverse transcriptase inhibitors 3TC, abacavir, and adefovir and to the protease inhibitor nelfinavir has been identified in one newly diagnosed, treatment naïve individual (0.2%).

• In Canada, HIV-1 subtype B continues to predominate with 91.6% of the samples subtyped (n=919) belonging to this group; subtypes A, C, D, E (also known as the recombinant A/E), recombinant A/B, and recombinant A/G have also been identified across Canada.

• There is geographic variation with respect to the prevalence of non-B HIV-1 subtypes. This variation is likely related to travel and migration from countries where other subtypes predominate.

Public Health Implications

• The prevalence of primary drug resistance can be used to develop population recommendations for initial therapies (especially for pregnant women and for use in post- exposure prophylaxis).

• The extent to which drug-resistant strains of HIV are being transmitted can serve as an indicator to evaluate the effectiveness of prevention programs.

• HIV isolates from different populations and changes over time can be monitored to evaluate diagnostic and screening algorithms to ensure that all circulating strains are adequately detected.

• HIV strain data can be used for research into and development of vaccines.

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